1. Technical Field
The present invention, involving image reading (scanning) apparatuses for reading image data in photocopiers, facsimile machines, computer networks, etc., relates to devices that scan both sides of an original-image document in the course of conveying the document from a sheet supply tray to a discharge tray.
2. Description of the Related Art
Generally, this kind of image reading apparatus is widely used as a device that scans original images in the course of conveying a document original sheet from a sheet supply tray to a discharge tray. Duplex scanning apparatuses that read images on one side of an original sheet in the course of the sheet's conveyance, then read images on the reverse side of the original are sheet are known. For the scanning means in such devices, photoelectric conversion elements are used, while line-sensors in reduction optics and contact-type line sensors in 1× optics are also known.
For example, Japanese Unexamined Pat. App. Pub. No. 2001-42578 proposes an apparatus configuration whereby an original sheet is conveyed from a sheet supply tray at an upper unit to a first platen at a lower unit, the upper and lower units being vertically disposed, and proposes providing a second platen in a path leading the original sheet to a discharge tray after images have been read at the first platen. A reduction-optics sensor is disposed at the first platen, and a 1×-optics sensor is disposed at the second platen. An original platen that is different from the first platen is provided in the lower unit to accommodate books or other types of thick or bulky originals. Ordinarily, these kinds of upper and lower units are configured to be able to open using a hinge unit. Specifically, the upper unit opens to allow an original to be placed on the platen.
Conventionally, if first and second image reading sensors are disposed in a path that guides the original sheet from the sheet supply tray to the discharge tray, a fixing means, such as screws, is used to mount the 1×-optics contact sensor to a sheet conveyance guide. The focal depth is shallower for contact sensors than it is for reduction-optics sensors, so mispositioning of the contact sensor causes improper focusing of the original and blurring of read images. Conventionally, however, when such sensors are fastened by screws to the guide plate on which original are conveyed, they can come out of their proper positioning by the repeated opening and closing of the apparatus. Furthermore, if it is difficult to remove dust or dirt adhering to image reading surface (platen) of the sensor, the sensor unit must be removed from the apparatus and cleaned. Conventionally, there was the possibility of scratching the reading surface when removing the sensor unit. Therefore, considerable skill and close attentiveness have been required in detaching the sensor unit.
Thus, the present invention provides an image reading apparatus that allows the easy mounting and removal of a sensor unit in an original sheet conveyance path with little or no mispositioning of the sensor unit at the upper unit side when the upper unit is repeatedly opened and closed over the bottom unit with the sensor unit mounted.